According to a 1981 report from New Jersey regulators, Trump used a popular tax code provision to report a negative income.

Trump has boasted about taking advantage of the tax code to pay as little as possible, but he's also made targeting those loopholes and the people and companies who use them a big part of his presidential campaign.

He's been increasingly reluctant to reveal his current tax returns, first claiming an Internal Revenue Service audit prevented him from disclosing them. According to several outlets, an audit doesn't legally prevent him from disclosing his past returns.

Now, Trump might become the first presidential nominee since the '70s to withhold his tax returns.